A semiconductor element has been conventionally mounted by a film carrier method. According to this film carrier method, semiconductor chips are connected via bumps to a film carrier tape which functions as a member for carrying a semiconductor element or for packaging same. A bump is a conductive protruding connection which is formed on an electrode surface of a semiconductor element as an inner bonding means to connect a lead on a film carrier and the electrode of the semiconductor element.
When forming a bump on the electrode surface of a semiconductor element, an adhesive metal layer of, for example, titanium and chromium, and a barrier metal layer of, for example, copper, platinum and palladium for the prevention of diffusion of bump metals, need to be formed on the electrode surface by sputter-etching, evaporation deposition and the like, and a bump of gold, etc. is formed thereon. As a result, the fabrication becomes extremely complicated. In addition, the semiconductor element and the electrode surface may be contaminated or damaged while forming bumps on the electrode surface.
It is suggested, therefore, to use, as a method not including a bump on the electrode surface of a semiconductor element, a method using a film having conductivity in the direction of the thickness of the film, i.e., a so-called anisotropic conductive film. Examples of such anisotropic conductive film include those containing conductive particles, such as carbon black, graphite, nickel, copper and silver, oriented in an insulating film in the direction of the film thickness and dispersed therein. However, this anisotropic conductive film is associated with difficulties in that insufficient orientation of the conductive particles leads to an uncertain electrical connection between the lead on the film carrier and the electrode of the semiconductor element, which in turn causes poor connection reliability.
It is also proposed to form a bump on the lead side of a film carrier to form a direct connection to the electrode of the semiconductor element. This method cannot cope with a fine-pitched or highly dense wiring of a semiconductor element, due to a difficulty in forming a circuit or bump necessary for such semiconductor element, as well as high level of caution necessary during connection operation.
In addition, a film carrier having a conductive circuit and a lead on the surface of an insulating film may be used. However, this method is again associated with potential difficulty in coping with miniaturization of semiconductor elements, since the area of outer lead bonding routinely becomes greater than the area of inner lead bonding, thereby making the final mounting area greater than the area of the semiconductor element.
A semiconductor element mounted on a film carrier is often protected by molding and sealing same with an insulating resin. When the film carrier has an exposed conductive circuit, however, an insulating sealant resin directly contacts said conductive circuit. The metal constituting the conductive circuit and the insulating resin adhere poorly to each other, allowing water in the air and other substances to intrude into the interface of the two to possibly degrade the reliability of the semiconductor device obtained.
Thus, a film carrier has been proposed which can sufficiently cope with a fine-pitched or highly dense wiring of a semiconductor element, can provide positive connections both in inner lead bonding and outer lead bonding, and which can make the mounting area as small as possible. The structure of this film carrier is that wherein a conductive circuit is not formed on an insulating film but completely embedded in the insulating film, an opening is formed in the insulating film to expose the surface of the embedded conductive circuit, and a conductor is filled in said opening to form a conductive path to allow electrical connection between the conductive circuit and the electrode of a semiconductor element or the landing part of an external substrate via the surface of this conductive path.
This structure is again associated with a problem in that the conductive path may come off from the insulating film when a defective semiconductor element is replaced after connection with the external substrate using solder, etc., due to a low adhesion strength between said conductive path and conductive circuit.
It is therefore an object of the present invention to solve the above-mentioned problems and provide a film carrier capable of sufficiently coping with a fine-pitched or highly dense wiring of a semiconductor element, providing reliable connections both in inner lead bonding and outer lead bonding, and decreasing the mounting area to the greatest possible extent, which provides superior adhesion between bumps and conductive circuits and enables suitable repair action.
Another object of the present invention is to provide a semiconductor device having the characteristics of the film carrier of the present invention after connection of the film carrier to a semiconductor element.